a. Field of the Invention
Broadly speaking, this invention relates to aviation. More particularly, in a preferred embodiment, this invention relates to methods and apparatus for providing a decelerated approach to a landing site, especially for rotary wing aircraft.
B. Discussion of the Prior Art
As is well known, the current technique for helicopter instrument landing approaches using conventional Instrument Landing Systems (ILS) is essentially the same as for fixed wing aircraft. That is, in making approaches to a runway equipped with an ILS, the helicopter pilot merely follows a gentle glideslope (e.g., 2.5 degrees) towards the runway maintaining a constant velocity down to "breakout" or visual acquisition of the ground and approach lighting systems. Only after "going visual" does the helicopter pilot decelerate his aircraft down to a slow taxi speed or hover.
Unfortunately, this approach technique is only useful for approaches to runway environments; such ideal circumstances are, however, seldom found in helicopter operations. Where the desired landing site is a confined area, a clearing in a forest, for example, the nearby presence of tall trees makes the use of a gentle (shallow) glideslope all but impossible and far more severe glideslope angles, for example, 6.degree. to 12.degree., must be employed. Thus, if the pilot is to make a landing approach to a confined area at night, with no lighting aids, or under conditions of reduced visibility, such as heavy rain, cloud cover or fog, a different approach technique must be adopted. It becomes quite clear that a helicopter pilot simply cannot track a 6.degree. or 12.degree. glidepath angle, break out at 50 feet above the ground while traveling at 60 knots, say, and bleed off the aircraft's forward and vertical speeds while continuing a straight-line approach to the confined touchdown area. While it is true that the invention disclosed herein was developed to lower the landing minima for helicopters during tactical military operations, one skilled in the art will appreciate that the results are equally applicable to civilian operations such as landing a helicopter at a forest-fire base obscured by smoke, at a fog-bound oil exploration field at sea, or at an inner city complex obscured by smog and haze, etc.